In the production of sugar from sugar beets, calcium oxide (lime), which is obtained by the thermal decomposition of calcium carbonate, is added to process liquors. In various stages of the refining procedure, carbon dioxide gas is introduced into the limed process liquors. This results in the production of a calcium carbonate precipitate, referred to as calcium carbonate sludge. This sludge is a byproduct of sugar production, and presents a waste disposal problem. The calcium carbonate sludge is generally of a very fine particle size, and cannot be readily recycled into calcium oxide in a conventional lime kiln. In some instances, special kilns may be employed to reconvert the calcium carbonate back to calcium oxide, which can subsequently be employed in the sugar refining process. U.S. Pat. Nos. 5,480,490 and 3,734,773 show such reclamation processes. However, the amount and extent to which such reuse and recycling may take place is limited, since the calcium carbonate sludge includes byproducts of the sugar refining process, and repeated reuse of the material results in a concentration of such contaminants in the process. As a consequence, sugar beet refiners find themselves faced with relatively large volumes of calcium carbonate sludge. Disposal of this material in landfills is both wasteful and expensive. Consequently, there is a need for a system or method which would allow for the economic reuse of this product.
Blasting processes are widely used for cleaning paint, corrosion and other contaminants from a variety of surfaces such as buildings, bridges, industrial equipment and the like. Blasting processes are also used to clean circuit boards and other electrical components. In a typical blast cleaning process particles of a blasting medium are entrained in a stream of high velocity gas, usually air, and directed against an object. Impingement of the medium removes surface contamination and coatings from the object. Typical blasting media comprise sand, glass, metal particles and plastic particles. A typical blasting process will generate a fairly large volume of used blasting medium, and the spent medium presents a significant disposal problem, particularly when it is contaminated with lead, chromium, cadmium paint residues and other industrial coatings which are generally classified as hazardous waste. As a consequence, spent blasting media must often be disposed of as hazardous waste, at high expense. In response to this problem, processes have been developed for decontaminating and/or recycling spent blast media, and one such process is shown in U.S. Pat. Nos. 5,372,650; 4,943,368 and 4,771,579. While such processes can be effective they are time consuming and expensive.
As will be explained in greater detail hereinbelow, the present invention provides a method whereby calcium carbonate sludge from a sugar beet refining process may be recycled so as to produce a high quality blasting medium.
Furthermore, the present invention provides for the recycling of contaminated blast media from various sources into a cement product. Thus, the present invention provides the unexpected result of solving two significant waste disposal problems while simultaneously extracting dual value from a heretofore problematic waste material.